One-third for the birds!

Atlantic puffin with sand lances.
[Image * Science/AAAS]

As the numbers of big fish like tuna decline, humans are increasingly catching anchovies, sardines and other small "forage fish" instead. But if humans take too many, they could be cutting off the food supply for the animals that prey on forage fish.

New research suggests that seabirds need about one-third of the world's forage fish for themselves. This knowledge should be helpful for deciding how much of the ocean's forage fish humans should catch. The authors of the study suggest that "one third for the birds" would be an easy way to remember their findings.

To figure out this number, Philippe Cury of the Institute de Recherche pour le Développement in Cète Cedex, France and an international team of coauthors analyzed population records for a variety of different forage fish and seabirds. (They included krill and squid because these are food sources for many other marine animals, even if they aren't technically fish.) The records spanned several decades and covered seven ecosystems within the Atlantic, Pacific and Southern oceans.

The authors found that the seabirds had fewer babies when levels of prey dropped below a certain amount, and this amount was remarkably consistent from one ecosystem to another. This amount represents approximately one-third of the forage fish in the world's ocean.

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This research appears in the 23 December 2011 issue of the journal Science.